The present invention relates to electromagnetic actuators or solenoids having an armature disposed for movement within a coil by electromagnetic forces generated upon flow of current through the coil. Solenoids of this type have found widespread usage in actuating electrically operated valves.
In solenoid actuators and particularly solenoid operated valves employed for controlling flow of fluid requiring relatively very low manufacturing costs, it has heretofore been the practice to provide a generally C-shaped pole frame or flux collector for providing a magnetic flux loop about the coil which is typically completed across air gaps through the armature. However, it has been found difficult to provide a simple low cost way of completing the flux loop and attaching the C-shaped flux collector to the coil in a manner that is robust and requires a minimum number of pieces in the assembly and yet provides the desired flux transfer. The problem is particularly difficult in solenoid actuators which are intended for use with a fluid control valve in which the armature is operatively connected to move a moveable valve member or obturator. Furthermore, it has been found difficult to assemble in high volume mass production the valve obturator with the valve body and armature and coil elements in a manner which is not cost prohibitive for low voltage automotive applications.
In automotive applications, the relative low voltage available from the power source requires a high number of turns of the coil for the available current in order to produce the required electromagnetic forces to effect armature movement for valve operation against the forces of the fluid supply pressure acting on the valve obturator. This difficulty in designing solenoids for such applications is further aggravated where there is poor flux transfer across the air gaps between the flux collector and the armature which is the result of the minimized surface area at the flux gap, which arises from the multiple piece construction of the pole frame and coil assembly. Thus, it has been desired to improve the magnetic flux transfer in a low voltage solenoid actuator assembly particularly for a fluid valve and to minimize the number of pieces and the manufacturing costs yet provide an assembly which is robust and suitable for the environment of automotive engine and transmission actuator service environment.